The present invention generally relates to flat panel displays, and more particularly relates to flat panel displays having an LED backlight, and even more particularly relates to methods and systems for controlling failure mode operations of LEDs in a flat panel display.
Recently, it has been proposed to use light emitting diodes (LEDs) to backlight liquid crystal displays (LCDs). It also has been proposed to utilized many strings of individual LEDs operating in series. Because an entire string of LEDs may fail if just one LED therein fails, or another single fault in the string occurs, designers have proposed to arrange the individual LEDs of each string in a widely scattered distribution. With this dispersion of individual LEDs in each string, the failure of a single string will not result in a visibly dark spot on the display, which would otherwise occur if the strings were arranged in concentrated groups.
While this design of employing widely scattered individual LEDs in each string has been used in the past, it does have some drawbacks. First of all, when a string fails, there is a slight reduction in the total brightness produced by the backlight. If many strings are used in a display, this degradation of brightness resulting from a single string failure may be slight and barely perceivable. In such situations, if another string were to fail, the brightness would again be reduced further. If the failures occur serially, i.e., one at a time, the viewer may not immediately recognize that one or more of the strings has failed. The backlight performance could continue to gradually decline until the brightness of the display becomes a serious problem. Secondly, if only a limited number of strings is used in the display, the failure of a single string will result in an immediately detectable degradation in backlight brightness. In certain critical applications, such as aviation electronics, this can be a serious problem.
Consequently, there exists a need for improved methods and systems for operating strings of widely dispersed individual LEDs in an efficient manner.
It is an object of the present invention to provide a system and method for operating an LED backlight in an efficient manner.
It is a feature of the present invention to utilize an optical feedback system.
It is another feature to include a dedicated sensor LED in each string of LEDs in the display backlight.
It is another feature of the present invention to include light sensor which measures the combined output of numerous sensor LEDs from the numerous LED strings.
It is yet another feature of the present invention to include a current measuring device in each of the strings for indicating that a string has failed.
It is an advantage of the present invention to achieve improved efficiency in operating LED backlights when a failure of a string occurs.
The present invention is an apparatus and method for controlling an LED backlight during failure modes, which is designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features, and achieve the already articulated advantages. The present invention is carried out in a xe2x80x9cdimming-lessxe2x80x9d manner in a sense that the adverse effects of an immediate dimming, upon the occurrence of a string failure, of the overall display brightness, have been greatly reduced.
Accordingly, the present invention is a system and method including an optical feedback mechanism which utilizes at least one LED in each string as an optical source for an optical brightness monitor.